Academic dissertation to be presented with the assent of the Doctoral Training Committee of Technology and Natural Sciences of the University of Oulu for public defence in Wetteri-sali (Auditorium IT115), Linnanmaa, on 26 April 2013, at 12 noon

Abstract

According to the EU’s strategy and the corresponding Finnish national strategy on waste materials, all kinds of waste must be utilised primarily as material (reuse, recycling) and secondarily as energy, and at the lowest level of waste hierarchy is their disposal using environmentally friendly methods. Today material efficiency is an essential topic in promoting sustainable use of natural resources, industrial by-products and waste material. The present goal proposed by the EU sets the target for the total proportion of renewable energy as high as 38% by 2020 in Finland. Up to 20 million tonnes of waste wood biomass per year are left unused in Finland, mainly in the forests during forestry operations, because supply and demand do not meet. As a consequence of high heat energy prices, the looming threat of climate change, the greenhouse effect and global as well as national demands to considerably increase the proportion of renewable energy, Finland currently has a tremendous interest in increasing decentralised pellet production alongside of large-scale factories.

The aim of this thesis is to promote the development of eco-, material- and cost-efficient Nordic wood-based pellet production and utilisation of pellet bio-ash by means of chemical research. Using Finnish wood (sawdust and shavings) as a model raw material, the total functionality of a pilot-scale pellet facility combined with an extensive chemical toolbox was tested in this study to promote development of an eco-, material- and cost-efficient wood-based pellet production chain. The chemical toolbox includes measurements of moisture content, density, heat value, mechanical durability and particle size distribution, TG analysis and elementary analysis, as well as new applications for pellet biodegradation using BOD OxiTop equipment and optical microscopic staining methods.

To improve the quality of pellets, considering the profitability of production and occupational safety factors (wood dust exposure, fire and explosion risk), it is profitable to use different binding agents, especially industrial by-products and locally utilisable residuals. Thus, lignosulphonate, residual potato flour and potato peel residue were used and tested as model adhesive binding agents. The results showed that binding agents increased the quality of pellets and changed their inorganic characteristics, but did not have a significant effect on their calorimetric heat values. Lignosulphonate even increased the rate of production. To characterise different starch-containing binding agents, a new specific optical microscopic staining method was developed and tested, and the initial results are presented in this thesis.

Wood pellet ash has potential as a liming agent, in soil remediation, as a soil fertilizer, and in granulated form, in new applications such as road construction and waste water purification. Valuable information about raw materials, binding agents and the pelletizing process is necessary when developing good-quality pellets—a prime biofuel—from non-utilised low-value and/or moist biomass that has undergone a cost-efficient drying process. This way pellet production will have more essential importance in energy policy, especially in the European forest belt.